Equine Endocrine Flashcards
Which layers make up the pituitary gland?
Pars Tuberalis
Pars Nervosa
Pars Intermedia
Pars Distalis
Which layer of the pituitary galnd is affected by PPID in the horse?
Pars intermedia
What is the Pars distalis regulated by (layer of pituitary gland)?
Neurotransmitters released from axons from hypothalamus
What is the Pars nervosa regulated by (layer of pituitary gland)?
Neurones. Direct axonal connection with the hypothalamus
How does PPID occur?
Loss of dopamine!
- Neurodegenerative lesion-loss of dopaminergic inhibition -> excess pars intermedia hormones (B-endorphins, CLIP, a-MSH, ACTH)
- Hyperplasia/adenomatous change to pars intermedia
What age of horses are usually affected by PPID?
15 years or older
What are the clinical signs of PPID?
Hirsutism (long hair coat) varies from delayed/abnormal shedding to thick curly coat Laminitis (50-80%) Sweating PUPD Weight loss and redistribution Wasted epaxial muscle and pot belly Bulging supraorbital fat Lethargy Susceptible to infections Rarely CNS effects (extension to brainstem)
How do you diagnose PPID?
Tier 1 tests:
-Basal ACTH (collect when horse is unstressed ie not after transport)
Dynamic endocrine tests:
-Low-dose dexamethasone suppression test (overnight)
If positive, begin tx. If inconclusive:
Repeat Tier 1 tests or do a Tier 2 test:
-ACTH response to TRH stimulation
How do you do a low-dose dexamethasone suppression test?
Take baseline serum cortisol Give 40ug/kg dexamethasone IM Retest cortisol 20 hours later If normal: cortisol levels should fall If PPID: cortisol levels fall slightly then rise
How do you do a TRH stimulation test (of ACTH)?
Particularly useful when horses with early PPID have normal resting ACTH
TRH causes the pituitary gland to release more hormones -> ACTH conc increases
Take a baseline serum ACTH
Inject 1mg TRH iv
Retest ACTH every 10 mins over an hour
Will get an increase in ACTH if PPID
What is the treatment for PPID?
Pergolide
Starting dose: 0.002 mg/kg/day
What should you monitor in horses with PPID to prevent them developing laminitis?
Insulin
Suggest a protocol for monitoring PPID
Baseline diagnosis
Monthly evaluation of ACTH and insulin for 3 months and if stable, 3-monthly evaluation for 9 months
More prolonged monitoring eg every 6 months in well-managed cases
Give some problems with high doses/increasing doses of pergolide when treating PPID
May cause inappetence
Laminitis/high insulin
How do you diagnose hypothyroidism in horses?
TRH stimulation test (different from PPID test-measure T3 and T4 4 to 5 hours later)
Feeding excess what can cause hypothyroidism?
Iodine
What is EMS?
Equine metabolic syndrome
Syndrome of obesity (generalised or regional), laminitis (or predisposition), and insulin resistance/hyperinsulinaemia
Give some factors that lead to insulin resistance in the horse
Obesity -> abnormal fat (fat starts acting like its own endocrine organ, releasing things it shouldn't) -Free fatty acids -Altered local glucocorticoids -Myostatin -Dysfunctional and pathogenic adipocytes -Impaired insulin signalling -Endothelial dysfunction Overfeeding, certain sugary grasses (eg rye grass)
Besides laminitis, what other hoof problems may a horse with EMS experience?
Frequent foot abscesses White line disease Lamella rings Seedy toe Dropped sole
Which horse breed is more genetically prone to EMS?
Dartmoor ponies
Why do horses with EMS get laminitis?
Prolonged hyperinsulinaemia -> damage to lamellae cells -> lose structure -> stretch and elongate -> rupture just underneath hoof wall
How can you diagnose EMS?
Resting hyperinsulinaemia (>20ulU/ml)
Combined IV glucose and insulin test
In-feed sugar tests (starve for 6-12 hours, give 1/2 scoop of forage chaff with 1g glucose powder per kg BW, take blood sample 2hr later and measure insulin. If insulin is >81mlU/L -> risk of laminitis)
What other findings may you find in horses with EMS?
Hypertriglyceridaemia
Mild elevation in basal cortisol
High blood pressure
Swollen sheath in males
How does EMS differ from PPID in its presentation?
Ponies/horses with EMS are younger than those with PPID
No hirsutism
Negative for PPID on dynamic and basal tests
How do you treat EMS?
Reduce obesity (predisposing factor)
Reduce hyperinsulinaemia
Treat and manage laminitis
Monitor response
How much hay should a horse have a day?
1.5% BWT hay (fresh weight)
How can you manage hyperinsulinaemia in horses with EMS?
Exercise
Diet
Drug therapy- Metformin, or Thyroxine
Where will a horse with laminitis be sorest?
Toe
What are the 4 grades of laminitis?
Grade 1: shifting
Grade 2: lame when walking
Grade 3: can’t pick up a hoof
Grade 4: can’t walk
What treatment would you recommend for laminitis?
Bute, ice may help reduce swelling, box rest to stabilise lamellae and prevent rupture, sole support eg deep bedding, loose sand, support hoof with softban/cotton wool
What is the normal range for blood glucose?
4-5 mmol/L
What is the normal range for blood insulin?
22 ulU/ml
How can you monitor a horses weight?
Weight tape
BCS
What do increased globulins indicate?
Inflammation
What does increased SAA (serum amyloid-A) and WBCs indicate?
Inflammation
